Giving to God what belongs to God
“So each of us shall give an account of himself to God.” Romans 14: 12
"Obey your leaders and submit to them; for they are keeping watch over your souls, as men who will have to give account.” Hebrews 13: 17
Vesting, improper
NOTE: Vesting may differ based on climate and culture. Local Bishops' Conferences or local Bishops may issue specific guidelines which vary from what is outlined here from the GIRM for the USA, the 2011 USCCB official English translation.
How a priest or deacon is vested at Mass shows respect for God and the Church. What is right and wrong in vesting? Vestments are addressed in the GIRM and include the following:
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Chapter IV
"119. In the sacristy, according to the various forms of celebration, there should be prepared the sacred vestments (cf. nos. 337-341) for the Priest, the Deacon, and other ministers:
"a) for the Priest: the alb, the stole, and the chasuble;
"b) for the Deacon: the alb, the stole, and the dalmatic; the latter may be omitted, however, either out of necessity or on account of a lesser degree of solemnity;
"c) for the other ministers: albs or other lawfully approved attire.
"All who wear an alb should use a cincture and an amice unless, due to the form of the alb, they are not needed."
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Chapter VI, part IV: Sacred Vestments, #335 - 347. Especially to be noted are the following:
"336. The sacred garment common to all ordained and instituted ministers of any rank is the alb, to be tied at the waist with a cincture unless it is made so as to fit even without such. Before the alb is put on, should this not completely cover the ordinary clothing at the neck, an amice should be used. The alb may not be exchanged for a surplice, not even over a cassock, on occasions when a chasuble or dalmatic is to be worn or when, according to the norms, only a stole is worn without a chasuble or dalmatic."
"The stole is a long cloth [...] that is worn around the neck like a scarf. It is secured at the waist with the cincture. [...] the stole reminds the priest not only of his authority and dignity as a priest, but also of his duty to preach the Word of God with courage and conviction [...] and to serve the needs of the faithful."
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Source: The Catholic Exchange
See the GIRM for more on vesting. Outside of the USA, vesting may differ. For example, in the Philippines, they have an indult allowing the stole to be worn over the chasuble under certain circumstances. See this Facebook comment.
"The practical purpose of the amice is to conceal the normal clerical clothing of a priest, and to absorb any perspiration from the head and neck. [...] The spiritual purpose [of the amice] is to remind the priest of St. Paul’s admonition: “Take the helmet of salvation and the sword of the spirit, the Word of God” (Eph 6:17)."
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Source: The Catholic Exchange
Redemptionis Sacramentum paragraphs 121-128 address vesting and include the following:
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123. "[...] the Priest, in putting on the chasuble according to the rubrics, is not to omit the stole. All Ordinaries should be vigilant in order that all usage to the contrary be eradicated."
126. "The abuse is reprobated whereby the sacred ministers celebrate Holy Mass or other rites without sacred vestments or with only a stole over the monastic cowl or the common habit of religious or ordinary clothes, contrary to the prescriptions of the liturgical books, even when there is only one minister participating. In order that such abuses be corrected as quickly as possible, Ordinaries should take care that in all churches and oratories subject to their jurisdiction there is present an adequate supply of liturgical vestments made in accordance with the norms."
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See Redemptionis Sacramentum for more on vesting.
Also see Father Edward McNamara, LC's posts in the EWTN Library: Main Celebrants Without Chasubles and Wearing Stoles Over the Chasuble. His post Albs, Stoles and Chasubles discusses differences seen in vesting among different religious orders.